The present invention relates to an improved magnetic head to be mounted adjacent the periphery of a drum which is rotated as magnetic tape is helically passed across the drum for helical recording or playback in a video tape recorder, audio digital tape recorder, etc.
Prior art magnetic tape recorders to the type contemplated by the present invention have a recording or reproducing track width of the order of several tens of microns.
The process for fabricating a magnetic head having such a small track width is hereinafter described with reference to FIGS. 1 and 2. As shown in FIG. 1, blocks 1a and 1b serving as two halves of a core are each worked on one surface to form a plurality of track width controlling grooves 16, and a gap forming thin film is formed on the respective gap defining surfaces 2a and 2b. Then, as shown in FIG. 2, the two blocks are joined together in such a way that the opposite grooves 16 are in registry. Thereafter, the grooves 16 are filled with a glass filler material 3 to form a single head block. This head block is ground and polished to provide a cylindrical surface that contacts the magnetic tape. The thus-worked block is sliced into discrete magnetic heads.
In the head fabrication process, it is important that the half blocks 1a and 1b be joined together with registry attained between the opposite track width controlling grooves 16. If misalignment occurs, the prescribed track width is not attainable.
The recent tendency is to decrease the track width defined by the magnetic heads in order to achieve a higher recording density. This has introduced even greater difficulty in joining together the two half blocks without loss of registry between the opposite track width control grooves 16.
To deal with this problem a magnetic head of the type shown in FIG. 3 has been proposed. This magnetic head is fabricated by the process depicted in FIGS. 4-7. First, blocks 5a and 5b serving as two halves of a core and which are not provided with any track width control grooves are prepared as shown in FIG. 4. After a gap-forming thin film is formed on each of the blocks, they are joined together to form a single core block 6a as shown in FIG. 5. This core block 6a is ground and polished to provide a cylindrical surface that contacts magnetic tape. Thereafter, grooves 17 are formed across the magnetic gap, except for a region corresponding to the track width (see FIG. 6), and the head block 6b is sliced along the center line of each groove 17 to form discrete magnetic heads as shown in FIG. 7.
Alternatively, a head block of the type shown in FIG. 3 may be produced by filling glass 18 in the grooves 17 in the head block 6b, which is thereafter sliced into discrete magnetic heads.
Because of the brittleness of the core material, chipping often occurs in the magnetic head shown in FIG. 7, either during the working of the head block or on account of sliding friction with the magnetic tape after it has been worked into the magnetic head. As a further problem the magnetic tape has a tendency to wear quickly since it contacts magnetic tape over a very small area.
A significant problem associated with the magnetic head shown in FIG. 3 is the great difficulty involved in achieving uniform filling of the grooves 17 with glass 18, and the resulting low production rate causes an undue increase in the price of the magnetic head compared with the product fabricated by the process illustrated in FIGS. 1 and 2.